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If a single-value keyword is followed by an empty string, the command unsets the variable for that keyword instead of setting it to the empty string. This is inconsistent and unexpected. Add policy CMP0174 which ensures the variable for a single-value keyword is always set when any value is given, not just for a non-empty value. The new CMP0174 policy only affects the PARSE_ARGV form of cmake_parse_arguments. The older form silently drops all empty string arguments before processing the argument list. Fixes: #25972
34 lines
1.5 KiB
ReStructuredText
34 lines
1.5 KiB
ReStructuredText
CMP0174
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.. versionadded:: 3.31
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:command:`cmake_parse_arguments(PARSE_ARGV)` defines a variable for an empty
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string after a single-value keyword.
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One of the main reasons for using the ``PARSE_ARGV`` form of the
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:command:`cmake_parse_arguments` command is to more robustly handle corner
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cases related to empty values. The non-``PARSE_ARGV`` form doesn't preserve
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empty arguments, but the ``PARSE_ARGV`` form does. For each single-value
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keyword given, a variable should be defined if the keyword is followed by a
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value. Prior to CMake 3.31, no variable would be defined if the value given
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was an empty string. This meant the code could not detect the difference
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between the keyword not being given, and it being given but with an empty
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value, except by iterating over all the arguments and checking if the keyword
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is present.
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For the ``OLD`` behavior of this policy,
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:command:`cmake_parse_arguments(PARSE_ARGV)` does not define a variable for a
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single-value keyword followed by an empty string.
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For the ``NEW`` behavior, :command:`cmake_parse_arguments(PARSE_ARGV)` always
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defines a variable for each keyword given in the arguments, even a single-value
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keyword with an empty string as its value. With the ``NEW`` behavior, the
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code can robustly check if a single-value keyword was given with any value
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using just ``if(DEFINED <prefix>_<keyword>)``.
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.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.31
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.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
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.. include:: STANDARD_ADVICE.txt
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.. include:: DEPRECATED.txt
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